This invention is concerned with a method and a system for communicating a plurality of mobile stations with an order station. This invention is suitable for use with an AVM (Automatic Vehicle Monitoring) method and system.
Conventionally, there are three methods for AVM, a dispersion transmitting method, a dispersion receiving method and a semiautomatic method. Constructions of these methods are shown in FIG. 6, 7 and 8 respectively.
In the dispersion transmitting method, there are many signposts 2 which are placed dispersively and from which is transmitted a position signal at all times. Further, the signpost 2 transmits an information from a communication station 1 toward inside of service area of each of zones A, B, C, D and E. A mobile station 4 receives a position signal from the nearest signpost which is one of the signposts 2a, 2b, 2c, 2d and 2e, and transmits an information of the position of the received signpost and the ID (identification) information toward an order station 3. The order station 3 receives position and ID information from specific vehicles so that it is able to know the zones in which the vehicles exist respectively.
In the dispersion receiving method, there are many signposts 2 which are placed dispersively. An order station 3 simultaneously calls all the mobile stations. When one of mobile stations 4 receives the call, the mobile station 4 transmits ID information. Each of the signposts receives the ID information from the mobile station 4 in the existing zone of the signpost and transmits a position information and the received ID information of the mobile station to the order station 3 on line.
In the semiautomatic method, an order station 3 simultaneously calls all the mobile stations. When one of mobile stations 4 receives the call, user of the mobile station 4 decides which zone the user is in, and the mobile station 4 transmits the zone information with ID information. The order station 3 receives the zone and the ID information from the mobile stations so as to know each of the mobile station's position.
These methods are described in Japanese Laid-open utility model No. 60-189149, and Japanese Laid-open patents No. 62-7230, No. 63-6698, No. 63-6700, etc. These prior art references disclose some communication arrangements for realizing the above 3 ways.
However, in above way, if the mobile station is out of zone and the order station 3 is not able to communicate with the mobile station, the position of the mobile station can not be known by the order station 3. For solving this problem, output power of the mobile station or order station requires higher power relative to the above 3 ways. But, if the high power is outputted, it brings high cost for the arrangement and it heads the decrease of the efficiency of the use of electric wave because the area used by one system should be expanded.